1. Field of the Invention
The invention relates to implantable brachytherapy devices. More particularly, the invention relates to improved brachytherapy devices, also known as radioactive therapeutic seeds, for the treatment of oncological and other medical conditions.
2. State of the Art
Radioactive seed therapy is a well known and well accepted medical procedure for the treatment of various oncological and other medical conditions. Seed therapy, also known as interstitial brachytherapy typically involves the implantation of one to one hundred relatively small capsules (seeds) into or around a treatment site. The capsules contain a radioactive isotope which irradiates the treatment site at close range without adversely affecting other parts of the body. Brachytherapy has been used successfully in the treatment of various types of cancers such as prostate cancer. It has also been used to prevent the growth or regrowth of tissues in the treatment of various occlusive diseases such as arteriosclerosis and arthrosclerosis subsequent to balloon angioplasty.
Radioactive therapeutic seeds are carefully designed to possess several important qualities. First, in the case of prostatic interstitial brachytherapy they should be relatively small, approximately 0.025 inch in diameter and approximately 0.16 inch long so that they may be implanted into the prostate gland using minimally invasive instruments and techniques. Second, the radioactive isotope must be enclosed in a biocompatible protective package since the seeds are typically not removed and will remain in the body for many years. Third, each seed preferably includes a radiopaque (e.g. high Z material) marker so that it can be located at the treatment site with the aid of fluoroscopy.
The state of the art of radioactive therapeutic seeds is substantially disclosed in seven U.S. Pat. No. 5,713,828 to Coniglione for "Hollow-Tube Brachytherapy Device", U.S. Pat. No. 5,405,309 to Carden, Jr. for "X-Ray Emitting Interstitial Implants", U.S. Pat. No. 4,891,165 to Suthanthiran for "Device and Method for Encapsulating Radioactive Materials" and U.S. Pat. No. 4,784,116 to Russell, Jr. et al. for "Capsule for Interstitial Implants", U.S. Pat. No. 4,702,228 to Russell, Jr. et al. for "X-Ray Emitting Interstitial Implants", U.S. Pat. No. 4,323,055 to Kubiatowicz for "Radioactive Iodine Seed", and U.S. Pat. No. 3,351,049 to Lawrence for "Therapeutic Metal Seed Containing within a Radioactive Isotope Disposed on a Carrier and Method of Manufacture", which are each incorporated by reference herein in their entireties. In addition, the art has been significantly advanced in co-owned U.S. Ser. Nos. 09/133,072, 09/133,081, and 09/133,082, which are hereby incorporated by reference herein in their entireties.
The Lawrence patent, which issued in 1967, describes many of the essential features of radioactive therapeutic seeds. Lawrence describes radioactive isotopes (I-125, Pd-103, Cs-131, Xe-133, and Yt-169) which emit low energy X-rays and which have relatively short half-lives. When implanted at a treatment site, these isotopes provide sufficient radiotherapy without posing a radiation danger to the medical practitioner(s), people in the vicinity of the patient, or other parts of the patient's body. Lawrence further describes a protective capsule which contains the isotope and prevents it from migrating throughout the body where it might interfere with healthy tissue. The capsule is cylindrical and made of low atomic number biocompatible materials such as stainless steel or titanium which do not absorb X-rays. The isotope is coated on a rod shaped carrier made of similar X23 ray transparent (e.g. low Z) material and is placed inside the capsule cylinder which is then closed. The other patents each provide some improvement over the original Lawrence design.
Despite the fact that radioactive therapeutic seeds have been in use for over thirty years and despite the several significant improvements made in the seeds, many concerns still exist regarding the use of the seeds. The seeds contain isotopes with relatively short half lives, and are not intended to be removed from the body. As a result, the therapeutic dose is determined by the amount of isotope provided in the seeds and the half-life of the isotope. While the problem has not been previously identified, there are instances in which it is desirable after implantation to further control the amount of radiation emitted and/or length of time which radiation is emitted by the seeds to the locus of implantation in the patient.
The ability, after implantation, to control the amount of radiation emitted by the seed is important for several reasons. First, the physician may desire to provide a high therapeutic dose of radiation for a relatively short period of time, and the decay period until the seed is considered ineffective as a radiation source may be deemed too long. Second, the implanted seed may be determined, e.g., via radiography, to have been implanted in a location at which radiation treatment is not desirable. Third, radiation from seeds implanted for treatment of prostatic cancer can cause irritation of the urethra and rectum. The physician may decide at some point in the treatment that the benefits of further radiation treatment at the prostate are outweighed by patient discomfort. Fourth, as sometimes occurs with the seeds, one or more seeds may be passed by the patient in a bowel movement or through the urethra during urination. The patient may collect the seed, but does not have a manner of safely storing or disposing the highly radioactive seed.
None of the art addresses any manner of deactivating or reducing the level of amount of radiation emitted by the seed after the seed is implanted in the patient.